Reduction of transmitted noise from hermetic compressors have long been a concern for domestic appliance manufacturers, particularly in compressors for refrigeration appliances.
Many of these appliances utilize reciprocating compressors. Referring to FIG. 1, a cutaway view of an example of a typical hermetic compressor 10 as installed in a refrigeration appliance is shown. The hermetic compressor 10 comprises a motor 12 having a crankshaft 14 coupled to a connecting rod 16. The connecting rod 16 is coupled to a piston (not shown) which is housed inside the cylinder head 18. The connecting rod 16, the piston and the cylinder head 18 together form the pump assembly 20 of the hermetic compressor 10. The pump assembly 20 and the motor 12 together form the compressor assembly 23.
During operation, the crankshaft 14 of the motor 12 rotates at a predetermined speed. This rotary motion is translated into a linear reciprocating motion via the connecting rod 16 coupled to the piston.
Noise is generated by the rotating motion of the motor 14 and also from vibrations of the reciprocating connecting rod 16 and piston of the pump assembly 20. This noise is partially suppressed by a hermetic shell 30 that encloses compressor assembly 23.
An oil lubrication system (not shown) is also incorporated into the hermetic compressor 10 for providing lubricating oil to the rotating crankshaft 14 of the motor 12 and other moving parts. The lubricating oil collects in the bottom of the hermetic shell 30 and the crankshaft 14 is partially submerged in the lubricating oil. The lubricating oil thus also acts as a transmission medium for vibrations from the compressor assembly 23 to the hermetic shell 30.
The hermetic shell 30 is typically supported by a mount 25 for installation within the refrigeration appliance. Noise and vibration can however be mechanically transmitted through the hermetic shell 30 via the mount 25 to the refrigeration appliance.
A refrigeration line system which carries refrigerant from the compressor assembly 23 for cooling the refrigeration appliance is also a source of mechanical transmission of noise. The refrigeration line system has a pipeline leading from the compressor assembly 23 that goes through the hermetic shell 30. A discharge line 22 is firmly attached to the hermetic shell 30 at points where the discharge line 22 goes through the hermetic shell 30. Noise and vibration of the compressor assembly 23 can thus be transmitted via the discharge line 22 out of the hermetic compressor 10.
Damping of vibrations from the hermetic compressor 10 have presently been done by mounting the entire compressor assembly 23 on suspension springs 40 inside the hermetic shell 30. The vibrations and noise are thus dampened by the suspension springs 40 before being mechanically transmitted to the mount 25 that supports the hermetic compressor 10.
The suspension springs 40 are further augmented by snubbers 45 which help maintain the integrity and shape of the suspension springs 40 and also prevent the suspension springs 40 from being displaced from their intended positions. The suspension springs 40 are typically helical springs made up of a plurality of coils having two opposing open ends which define a circular tubular space within their helix shape. The snubbers 45 can be described to be substantially cylindrical and are typically small protrusions that fit into the open ends of the suspension spring 40.
Referring to FIG. 2, the snubbers 45 are typically used in pairs for each suspension spring 40. An upper snubber 45a is attached to the compressor assembly 23 and a corresponding lower snubber 45b attached to the lower portion of the hermetic shell 30. The upper snubber 45a is substantially aligned with the lower snubber 45b and allows the upper snubber 45a to be fitted into one end of the suspension spring 40 and the lower snubber 45b to be fitted into the opposing end of the same suspension spring 40.
For ease of manufacturing and assembly, the suspension spring 40 is firmly attached to at least one of the snubbers 45. This allows for ease of fitting of the corresponding upper snubber 45a or lower snubber 45b into the opposing open end of the suspension spring 40.
However, this firm attachment of the suspension spring 40 to at least one of the snubbers 45 have a noise frequency of around 500 Hz. When this noise frequency coincides with operating frequencies of the hermetic compressor 10, the total noise and vibration experienced will be amplified and cause a substantial noise concern.
Furthermore, interference fit between the suspension spring 40 and the snubbers 45 changes the noise resonance frequency as the interference fit changes. The interference fit is the amount of tolerance or space between the suspension spring 40 and the snubbers 45.
Therefore, a need clearly exists for a method and apparatus that reduces the noise transmitted from compressors, or at least alleviate limitations of existing damping techniques.